This invention relates to oxidation and/or ammoxidation catalysts containing the elements bismuth, molybdenum, antimony, vanadium and oxygen, and optionally containing one or more additional metal elements and to a method of preparing such catalysts. In another aspect, this invention relates to a process employing such catalysts.
It is well known that olefins can be oxidized to oxygenated hydrocarbons such as unsaturated aldehydes and acids, for example, acrolein and methacrolein, and acrylic and methacrylic acid. It is also well known that olefins can be ammoxidized to unsaturated nitriles such as acrylonitrile and methacrylonitrile. The value of such oxygenated hydrocarbons and unsaturated nitriles is generally well recognized with acrylonitrile being among the most valuable monomers available to the polymer industry for producing useful polymeric products.
Various catalytic processes are known for the oxidation and/or ammoxidation of olefins. Such processes commonly react an olefin or an olefin ammonia mixture with oxygen in the vapor phase in the presence of a catalyst. For the production of acrolein and acrylonitrile, propylene is the generally used olefin reactant and for the production of methacrolein and methacrylonitrile, isobutylene is the generally used olefin reactant. Many catalysts are disclosed as suitable in the foregoing reactions. One such catalyst is described in Example 3 of U.S. Pat. No. 3,681,421. This catalyst employs oxides of antimony, vanadium, and at least one additional polyvalent metal which may be titanium in the proportion of 1 gram of antimony, 0.12-0.5 gram atoms of vanadium, and 0.25-0.5 gram atoms of titanium. Under the conditions of that example, a yield of 56% of acrylonitrile was obtained using propylene, ammonia, air and steam as reactants.
Further, U.S. Pat. No. 4,062,885 discloses the preparation of phthalonitrile by ammoxidation of ortho-xylene in the presence of a supported catalyst of the general formula Bi.sub.a Sb.sub.b Mo.sub.c V.sub.d O.sub.x wherein a=1-20, b=1-10, c=0.1-15 and d=1-20. Use of such a catalyst for oxidation or ammoxidation reactions involving unsaturated aliphatic hydrocarbons is not mentioned, however.
More recently, U.S. Pat. No. 4,093,558 discloses oxidation catalysts composed of the oxides of antimony, molybdenum, at least one of iron and vanadium, and, optionally, an additional element which may be bismuth. These catalysts are useful for manufacture of maleic anhydride from butane.
Preparation of ammoxidation catalysts by preforming bismuth molybdate and then mixing the preformed bismuth molybdate with other elements is disclosed in U.S. Pat. Nos. 4,040,978, 4,148,757 and 4,212,766.
It is well known that the economics of acrylonitrile manufacture dictate increasingly higher yields and selectivity of conversion of the reactants to acrylonitrile in order to minimize the difficulties attending purification of the product and handling of large recycle streams. Moreover, it is known that prior art catalysts frequently produce relatively large quantities of undesired oxygen-containing by-products such as CO.sub.2, acrolein and/or acrylic acid which must be removed in purification of the acrylonitrile.